I doubt we'd last a year. Most plants would either die or go dormant inside of a month or so; the animals which live on them, a month or so after than. Meanwhile, it'll start to cool off fairly quickly, as surface heat is radiated into space but no more is coming in. We'd enter a permanent winter within a couple months, and the temperature would continue to drop steadily. At some point, the temperature will bottom out as the heat leaking out from under the crust balances out what gets radiated away, but at that point, most higher life will be dead anyway. After a few (hundred?) million years, even the core will cool off enough so that the atmosphere will freeze out, leaving a bleak, dead world.

I doubt we'd last a year. Most plants would either die or go dormant inside of a month or so; the animals which live on them, a month or so after than. Meanwhile, it'll start to cool off fairly quickly, as surface heat is radiated into space but no more is coming in. We'd enter a permanent winter within a couple months, and the temperature would continue to drop steadily. At some point, the temperature will bottom out as the heat leaking out from under the crust balances out what gets radiated away, but at that point, most higher life will be dead anyway. After a few (hundred?) million years, even the core will cool off enough so that the atmosphere will freeze out, leaving a bleak, dead world.

Why are you so optimistic? We'd all be dead within a few weeks. The Earth would cool quickly and wouldn't stop until it reached the temperature of deep space (-270C or 3K). The warmth from the oceans might buffer this effect in places on Earth.
We'd be lucky to rely on power stations to supply our homes with heat. I think there might be enough food reserves to last longer than a week but our main concern would be freezing to death.
Another thing you would notice is that it would snow continously. As the air cools, it would no longer be able to hold its moisture.

It might be possible for a relatively small number of people to survive for some years using fossil fuels for heat and lighting. Inside a coal mine might be good, with occasional forays to the surface to scavenge. But only a few very lucky and inventive people would be able to do this, and even they might find things getting tougher and tougher as surface temnperature dropped.

Sans Sun, the Earth would freeze rapidly. We're not talking about Antarctic winter cold, either, but cold like Triton. The atmosphere isn't thick enough to provide much of a thermal blanket, nitrogen which comprises the bulk of the atmosphere would turn liquid, and possibly the oxygen as well until the atmosphere achieves a temperature/pressure equilibrium, leaving only a tenuous atmosphere of residual oxygen and nitrogen, maybe a little methane, plus whatever trace gases don't freeze. Cigarette smokers, careful where you throw those butts; that liquid oxygen will cause easy fires, though they probably won't last too long as the free oxygen will rapidly combine with any carbon compounds.

I once started to run a back-of-the-envelope calcuation based purely on radiative loss, and then realized that the emissivity will change dramatically once atmospheric gases start to condense. (I also couldn't find an agreed upon number for the thermal load of the Earth, though I'm sure that climatologists or geophysicists must have a standard estimate.) Finger-in-the-wind guess is days rather than weeks, and certainly not months before you're completely frozen. The amount of geothermal heating on the surface of the Earth is negligable, and energy loss will be progressive. Dirt is not an especially good thermal conduit, so it would take a while to cool but evaporative cooling as the atmosphere condenses will leach heat out quick, turning it into a tundra. The oceans might survive a bit longer, especially if an adiabatic layer of ice forms over and traps in the remaining liquid.

The only hope for the long term would be to enhance volcanism in an attempt to produce environmental heat. I'm not a geophysicist, nor do I play one in Intuitor.com's #1 Insultingly Stupid Movie Physics Classic, but I doubt you could get anything like enough heat to keep the atmosphere from freezing, much less make the surface habitable, so you'd have to tap the thermal energy to keep your underground shelters warm. (You wouldn't want to live on the surface because lacking an atmosphere you'd be at hazard to meteor bombardment and cosmic radiation that is too energetic to be deflected by the magnetic field.)

Most people would die within the first few days to a week from the cold, and of those that are left, most will die within a year from starvation. Meanwhile, of course, everyone who hasn't died yet are going to be fighting with each other to try to make sure they stay in that category. So in that sense, civilization would crumble pretty quickly.

However, you'd probably have some remnant vestige of humans, carrying on some sort of civilization, indefinitely. A few folks would be able to improvise arrangements where they could heat and light small areas where humans and their crops could survive. Eventually, these folks would meet up with each other, extend the artificially-powered areas, and somewhat repopulate the planet.

__________________
Time travels in divers paces with divers persons.
--As You Like It, III:ii:328

As it is, entire communities of people are able to survive in northern Alaska for 2-3 months with no sunlight. However, those people are well prepared for those conditions compared to most of the rest of the Earth's population. Billions would die in the first few weeks after no sunlight. Organized civilization in the mainstream world would end almost immediately.

A few of those who are better prepared* could likely last a few months until food supplies ran out.

*are well stocked on non-perishable foods, have weapons, experienced in cold weather survival, have sub-zero clothing, do not need medication or other accomodations of modern society, and have a well insulated building or bunker.

As it is, entire communities of people are able to survive in northern Alaska for 2-3 months with no sunlight. However, those people are well prepared for those conditions compared to most of the rest of the Earth's population. Billions would die in the first few weeks after no sunlight. Organized civilization in the mainstream world would end almost immediately.

A few of those who are better prepared* could likely last a few months until food supplies ran out.

*are well stocked on non-perishable foods, have weapons, experienced in cold weather survival, have sub-zero clothing, do not need medication or other accomodations of modern society, and have a well insulated building or bunker.

It would seem to me that once it got cold enough, cars would not start, no one would be able to move, food deliveries would cease, and in addition to the cold killing off a lot of people, the elimination of food supplies would also spell doom very quickly. Pipes would freeze so water would no longer be available either.

Well, it's not that GREAT a question. A more plausible approach to a similar problem would be asking what would happen after a massive nuclear exchange kicked up sun-obscuring clouds of dust that lasted for years (something that a great many people spent a great many hours thinking about), or the strike of a massive comet causing a dinosaur-ish extinction event (which could happen without warning at any second, even before I finish this sentence.... phew, made it).

Personal survival would depend hugely on being lucky enough to be close to, say, a hydroponic farm complex powered by a nuclear reactor. One might be able to last for years until the environment recovers. However, having the sun disappear means it all academic - long-term survival is moot. Some humans might hobble along a few years or decades, but the end is inevitable.

This is a Straight Dope perennial, someone asks a variant of this question a couple times a year. Someone might dig up some of the old threads.

But basically you've got a week or maybe two before things cool down to Antarctic temperatures all across the planet. Once you hit 60 below (the coldest it gets in my old hometown of Fairbanks AK) lots of ordinary technology just stops working. Cars won't start anymore, water lines freeze up, metal and plastic items snap in half, outside fuel tanks clog and fuel lines freeze solid.

Even running your furnace night and day won't help much if you don't have an insulated house. And of course, you're not going to get many more fuel deliveries, even if the heating oil company has fuel on hand they're not going to give it to you. And the furnace won't be much help once the atmosphere starts freezing out, even if you had essentially unlimited fuel and an airtight shelter, you need oxygen to run the furnace.

If you had the time before you froze to death, you could rig up a method of shoveling up frozen air and heating it for intake into your furnace system, but frozen air is going to be a limited resource. I'm not sure how thick an average layer is going to be, but once the bulk of the atmosphere is frozen out you're not going to get any new deliveries. You'd have to send your air gathering machine farther and farther into the field.

If you were at a nuclear reactor you might be able to live until you starved to death. They have machine shops and engineers and technical people, I imagine they might be able to fabricate shelters heated electrically from the plant, and the plant itself might have enough fuel on hand to last quite a long time. There might be frozen food supplies left after most people have frozen to death. But scavenging that is going to be very hard, especially with no air. You can drive a car at 60 below as long as it starts warm. But a IC engine needs air. And you'll need the equivalent of spacesuits to walk around. Perhaps these could be manufactured.

Ironically, places near arctic would be the best equipped for survival, it would be funny if the last surviving humans were the ones at the base at the south pole.

Someone said that the sun would actually increase in size, and that Earth would be drawn to it and vaporize. Google how the sun works and then fate of the sun.

Well, if you're talking about the Sun after its standard Main Sequence lifespan and into the red giant phase (about another 4-5 Byr), then yeah, the outer layers of the Sun will start to expand as hydrogen fusion ramps down; they'll be pretty cool, actually, but will eventually ungulf the Earth and prevent it from radiating heat away. Plus, as the Sun starts hydrogen fusion, then the C-N-O cycle the radiant temperature will increase. This won't "vaporize" the Earth, but it will probably drive off all volitiles and boil the oceans away, leaving it a lifeless rock circling a (greenish) white dwarf star that is slowly fusing the remaining elements into silicon, phosphorus, sulfer, chlorine, argon, et cetera on up to iron. An ignominious end for our favorite star.

This is a Straight Dope perennial, someone asks a variant of this question a couple times a year. Someone might dig up some of the old threads.

But basically you've got a week or maybe two before things cool down to Antarctic temperatures all across the planet. Once you hit 60 below (the coldest it gets in my old hometown of Fairbanks AK) lots of ordinary technology just stops working. Cars won't start anymore, water lines freeze up, metal and plastic items snap in half, outside fuel tanks clog and fuel lines freeze solid.

Even running your furnace night and day won't help much if you don't have an insulated house. And of course, you're not going to get many more fuel deliveries, even if the heating oil company has fuel on hand they're not going to give it to you. And the furnace won't be much help once the atmosphere starts freezing out, even if you had essentially unlimited fuel and an airtight shelter, you need oxygen to run the furnace.

If you had the time before you froze to death, you could rig up a method of shoveling up frozen air and heating it for intake into your furnace system, but frozen air is going to be a limited resource. I'm not sure how thick an average layer is going to be, but once the bulk of the atmosphere is frozen out you're not going to get any new deliveries. You'd have to send your air gathering machine farther and farther into the field.

If you were at a nuclear reactor you might be able to live until you starved to death. They have machine shops and engineers and technical people, I imagine they might be able to fabricate shelters heated electrically from the plant, and the plant itself might have enough fuel on hand to last quite a long time. There might be frozen food supplies left after most people have frozen to death. But scavenging that is going to be very hard, especially with no air. You can drive a car at 60 below as long as it starts warm. But a IC engine needs air. And you'll need the equivalent of spacesuits to walk around. Perhaps these could be manufactured.

Ironically, places near arctic would be the best equipped for survival, it would be funny if the last surviving humans were the ones at the base at the south pole.

What about the validity of the theory that the Sun would expand and the Earth would be sucked into it and vaporize, frying us all, as per How Stuff Works.com - "How The Sun Works" - "Fate of the Sun"?

Ironically, places near arctic would be the best equipped for survival, it would be funny if the last surviving humans were the ones at the base at the south pole.

Frederik Pohl's Hugo Award winning "Fermi and Fire" postulates just such a thing, and has the characters living (and eventually dying) at a geothermal power facility in Iceland after a full scale nuclear exchange and resulting climate change. I have a few issues with the stated dire projections of the Nuclear Winter Hypothesis, but it's a fantastic story.

What has Wolf 359 ever done for me? Heck, it's fainter than can be seen from Earth by several orders of magnitude, and even if you could get in orbit of it, it's a M6 variable that is unlikely to have any habitable zone. Now, Tau Ceti might be kind of interesting (although the system appears to be metals poor) but Sol wraps me in her warm yellow embrace almost every day in sunny Southern California, so I have a great affection for and loyalty to her.

Is the sun massive enough to get all the way to iron? Seems to me that it'd have to be about 40% more massive to pass the Chandresekhar Limit and be able to fuse anything beyond oxygen, neon and magnesium.

Frederik Pohl's Hugo Award winning "Fermi and Fire" postulates just such a thing, and has the characters living (and eventually dying) at a geothermal power facility in Iceland after a full scale nuclear exchange and resulting climate change. I have a few issues with the stated dire projections of the Nuclear Winter Hypothesis, but it's a fantastic story.

Is the sun massive enough to get all the way to iron? Seems to me that it'd have to be about 40% more massive to pass the Chandresekhar Limit and be able to fuse anything beyond oxygen, neon and magnesium.

Chandrasekar's Limit (~1.44 Solar masses) is the limit at which electron degenercy pressure is overcome by gravitational compression and the particles start violating the Pauli exclusion principle. When this occurs...well, honestly, we don't properly know what happens when this occurs; speculation has the particles turning into a blob of pure neutrons, a quark-gluon mash, or some kind of high temperature gage boson condensate with free quarks bobbing around, or who knows what. Note that even before then and after this point the normal matter on the outer layers will continue to fuse until it condenses or is transmuted to iron, or otherwise blown off by the flaring, variable output of the fusion reactions.

Note that 1.44 Solar masses is the mass of the resultant dwarf star, not the original star from which it comes before blowing off a portion of its mass. (A dwarf that feeds off of a companion start and goes nova can conceivably lose more mass than it accreates via helium flashes.) At a somewhat higher mass (>3-4 Solar masses) the star goes supernova and blows off a significant amount of mass in a quick chain of reactions. At somewhat higher mass (depending on the composition of the star) it folds into itself and becomes a singularity.

And yes, the Sun will fuse elements all the way up to iron, albeit with increasing inefficiency as it moves up the fusion chain. At anything past the C-N-O cycle the fusion reactions are driven by rapid gravitational pressure and contraction, and are increasingly unstable, providing little luminous output.

Frederik Pohl's Hugo Award winning "Fermi and Fire" postulates just such a thing, and has the characters living (and eventually dying) at a geothermal power facility in Iceland after a full scale nuclear exchange and resulting climate change. I have a few issues with the stated dire projections of the Nuclear Winter Hypothesis, but it's a fantastic story.

Stranger

There is also a short story called "A Pail of Air" about a family that survives after the earth is pulled out of its orbit and cools so quickly that the atmosphere solidifies on the ground. (The title is a reference to the characters scooping up a pail of liquid oxygen for breathing.)

I'd like to ask a somewhat related question, now that things are expanding a bit. I know it's really dumb and I'm missing something obvious, but I've never understood why winters are so cold compared to summers. Isn't it the case that the only difference is that the hemisphere is tilted away, rather than toward, the sun? And if that tiny bit of difference in distance can make that much difference in temperature, then why wouldn't a sunless earth degenerate to Triton temperatures in a few hours?

I'd like to ask a somewhat related question, now that things are expanding a bit. I know it's really dumb and I'm missing something obvious, but I've never understood why winters are so cold compared to summers. Isn't it the case that the only difference is that the hemisphere is tilted away, rather than toward, the sun? And if that tiny bit of difference in distance can make that much difference in temperature, then why wouldn't a sunless earth degenerate to Triton temperatures in a few hours?

In winter you're getting less solar radiance, and at a lower angle throughout the day, than in summer. And this happens across the entire hemisphere. The effects in climate are far more complex than just a difference of 47° of tilt (summer to winter) of course, but that's the key component in seasonal variation.

Air streams, and thus, heat, don't cross the equator much, so a loss of heat in one hemisphere doesn't mean energy will be automatically transferred to the other side hemisphere to obtain a thermodynamic balance like it would in a simple system. Most heat is held by and transferred by ocean currents anyway. The Gulf Stream in the Atlantic and the corresponding circulatory loop in the Pacific serve to warm Western Europe and Western United States, respectively, making those areas considerably warmer and wetter than corresponding inland and easterly regions. Other geological features, along with larger global thermohaline circuits, serve to moderate the loss or gain of additional thermal radiation as the Earth wobbles its way around the Sun.

On the question of time, you'd have to perform a very sophisticated analysis to offer an accurate assessment of what would occur if the Sun totally blinked out; as atmosphere becomes drier (reducing cloud cover and resulting internal and external albedo) the emissivity of the Earth (i.e. its ability to radiate energy) will change, and as it changes, it'll create feedback loops (probably posivite ones) that will continue to feed those behaviors. I'd suspect at some point that oceans would freeze over, which would both reduce available humidity sources and sources of environmental head, but at the same time retain head in the ocean deeps, allowing creatures to survive for a while at least. I'd guess only a few days of habitability on the surface, at best, before temperatures become so frigid that sustaining life becomes impossible. After that, nitrogen will start to freeze out (77K). Thermal loading and geothermal heat should keep the Earth well above the 2.7K microwave background for centuries if not millenia, and might prevent oxygen from liquidizing (54K) for some period of time, at least.

So, if you know anything that's about to go down with the Sun...you'd better build yourself a shelter next to a geothermal vent and stock it well.

a lifeless rock circling a (greenish) white dwarf star that is slowly fusing the remaining elements into silicon, phosphorus, sulfer, chlorine, argon, et cetera on up to iron. An ignominious end for our favorite star.

Nitpick: Fusion of metals (in this context, anything more massive than helium) occurs quickly or not at all. A star's helium-burning phase is only about a tenth as long as its hydrogen-burning phase, and iron formation occurs on a timescale of order seconds, as a star goes supernova. A white dwarf is no longer burning anything at all, and continues to glow only as long as it has leftover heat to radiate.

What about the validity of the theory that the Sun would expand and the Earth would be sucked into it and vaporize, frying us all, as per How Stuff Works.com - "How The Sun Works" - "Fate of the Sun"?

Well, of course in reality it is physically impossible for the sun to just stop shining. All the energy in the sun has to go somewhere.

So for the Sun to just disappear would require alien space bats MAKING the Sun disappear. Maybe they create a Dyson shell around the sun, and no visible light radiates out. Eventually though the shell will start radiating in the IR, probably not enough to keep the Earth from freezing, but maybe enough to keep the air from liquifying. Or maybe the rotate the Sun through a couple of dimensions, or maybe they do the same for the Earth, ala "Have Space Suit, Will Travel". Or you turn the Sun into a black hole, same mass but doesn't undergo fusion and doesn't radiate much visible light. If you do it right lots of the energy of the Sun could be trapped under the event horizon, do it wrong and the earth will be fried by all sorts of superenergetic photons and exotic particles. Or send a rogue mass through the solar system precisely calculated to send the Earth flying out into interstellar space. But you've got to do this exactly right. If you just want to KILL ALL HUMANS it would be 1,000,000 times easier just to send a much smaller mass slamming into the Earth. That's the thing, any aliens that could turn off the Sun could KILL ALL HUMANS in very simple easier ways. Maybe they want to preserve Earth for study, I suppose.

I always wonder if anyone has discovered any objects that radiate in the IR that could be Dyson shells. Maybe so-called "red giants" are Dyson shells that use most of the visible, and what we see is merely the waste heat radiating out into space.

The sun is most definitely going to become a red giant. There is no question, scientifically-speaking, about that. The predicted sequence of stages for stars with mass similar to that of the sun is pretty solid. And pretty much all estimates I've heard for the diameter of the red giant that will be our sun have the first three planets (yep, that's us) engulfed inside of it and Mars being planet numero uno.

I would imagine a nuclear sub could last until the food runs out. Then the sailors turn to cannibalism. Interesting problem, because you have to feed some crewmembers to other future stewpot-bound crewmembers to keep them alive long enough for you to eat them later. Lots of inefficiency built into the system, kind of like a multistage rocket. I suppose the sub will have some empty freezer space once the food starts to run out, best to kill and freeze as many crewmembers as possible as soon as possible.

If you could figure out a way to harvest tubeworms from the deep ocean vents you might last until you run out of reactor fuel. But I don't think this is possible, most likely you'll starve to death. Although...as the oceans freeze over you'll be forced deeper and deeper to stay out of the ice. It could be the submarine will be forced deep enough for the hull to give out before the food gives out. We'd have to have some wild guesses for how fast/how thick the ice forms, and I suppose the exact depth when a given nuclear sub implodes is classified information.

I had the idea that the sub should surface immediately to stay on top of the ice, but then I recalled that the reactors on the subs take in liquid water for cooling, which means you won't be able to keep the reactor going. Plus, underwater you've got the warm water buffering your temperature, on the surface you've just got the thin metal skin exposed to two-digit Kelvin temperatures.

So for the Sun to just disappear would require alien space bats MAKING the Sun disappear. Maybe they create a Dyson shell around the sun, and no visible light radiates out. Eventually though the shell will start radiating in the IR, probably not enough to keep the Earth from freezing, but maybe enough to keep the air from liquifying...I always wonder if anyone has discovered any objects that radiate in the IR that could be Dyson shells. Maybe so-called "red giants" are Dyson shells that use most of the visible, and what we see is merely the waste heat radiating out into space.

Two points: first of all, a star radiating in only the IR bands would be an obviously artificial construct from its spectral lines. Even brown dwarfs radiate as (weak) radio sources (which your presumably metal shell would screen). Second, a "Type II" Dyson sphere (which is not Freeman Dyson's original concept of a vast number of habitats orbiting a central star in an enclosing orbit, but a single static spherical shell with the star at the center), which I believe is what you are referring to, is dynamically unstable. Because there is no net force due to gravitation inside of a hollow sphere, any relative difference in motion between the star and the sphere (say, asymetrical meteor impacts) will cause one to impact the other. Without an active control system, instability and contact is inevitable. So, Dyson spheres are unlikely.

Also, constructing a Dyson sphere in a system like our solar system would certainly require more materials than are available, even if you could reduce the gas giants to construction materials, so you'd have to drag materials from extrasolar sources, which seems like a pretty pointless waste of energy. More than likely by the time you have anything like that capability, you'll be less interested in controlling an individual star and more flitting about on your Improbability Drive and discussing what cut of steak to have with the Dish of the Day.

Well, I used the term "shell", because nowadays it seems the term "Dyson Sphere" means a "solid" (of course it couldn't really be solid) sphere with a biosphere inside. Of course, you'd have to have gravity generators and such, and on and on. A not-neccesarily continuous collection of objects surrounding a star such that only a small fraction of the visible light escapes into interstellar space is what I was thinking of. The ASBs could just set up an incredibly extensive chain of solar power satellites orbiting the Sun along the ecliptic around the orbit of Venus, using the mass of Venus and Mercury. You wouldn't need much to block 99% of the solar radiation to Earth.

Well, I used the term "shell", because nowadays it seems the term "Dyson Sphere" means a "solid" (of course it couldn't really be solid) sphere with a biosphere inside. Of course, you'd have to have gravity generators and such, and on and on. A not-neccesarily continuous collection of objects surrounding a star such that only a small fraction of the visible light escapes into interstellar space is what I was thinking of. The ASBs could just set up an incredibly extensive chain of solar power satellites orbiting the Sun along the ecliptic around the orbit of Venus, using the mass of Venus and Mercury. You wouldn't need much to block 99% of the solar radiation to Earth.

The Sun is about 1.4M km in diameter, and the Earth is 12,800 km. A disk large enough to mask the Sun, orbiting at .85AU (between the orbit of Venus and Earth) would have to be 220x103 km in diameter, or a little more than 17 times the diameter of Earth. This would have a surface area of about 38x109 km. Given concrete with a thickness of ~1m, this would mass 9.2x1019 kg; 1 Ceres or one of Jupiter's Galilean moons should cover it. The closer you move it to the Sun, the worse it gets. Plus you've got a problem: its free orbit is going to be of significantly shorter period than Earth; therefore, you're either going to have to have it under constant acceleration to keep it in place, or you're going to have to build a ring structure and spin it at the desired rate of rotation (which, in any case, will have to vary during different stages of the Earth's orbit). You're also going to have to figure out how to keep it on station, as we all know that a ring structure spun around a central mass is unstable. And the tension in the structure is going to be beyond the tensile strength of any known material by many orders of magnitude.

If you place your sunshield at the Sol-Earth L1 libration point, the minimum size of a global parasol would be about 27,000km in diameter. This would be the ideal place to put it, rather than in between planetary orbits; it should stay in position with minimal orientation maneuvers and not requiring any thrust or special mechanism to stay on station, plus you could give it a keel pointing toward the Earth that would keep it properly oriented (more or less) by tidal forces. This would only mass about 65x106 tonnes (assuming a flat, 1 meter thick disk, the minimal shape), which could be supplied by a mid-sized Near Earth Object (asteroid). That puts it in the realm of just slightly absurd conjecture rather than highly improbable fantasy.

Either way, it isn't going to block radiation going out to the universe at large. A true Dyson sphere (be it a Type I collection of individual habitats, or a Type II solid sphere) is going to require massive amounts of material beyond what is found in a system like ours.

But why do we insist that the system of shrouds be 1 meter thick? Why not submillimeter thick? You make the screens out of the ASB equivalent of superconducting mylar film. Then you get several layers of solar power satelites freely orbiting around the sun, no rings needed.

I'm not imagining "habitats", I'm imaging ultrawispy solar collectors. Or mirrors bouncing most of the photons back into the sun. Although they're gonna radiate back out again sometime. This is why I was imagining that the shell of solar collectors is going to look like a red giant...eventually those solar collecters are going to be glowing red hot.

There is also a short story called "A Pail of Air" about a family that survives after the earth is pulled out of its orbit and cools so quickly that the atmosphere solidifies on the ground. (The title is a reference to the characters scooping up a pail of liquid oxygen for breathing.)

By Fritz Lieber, by the way.

Only on the Dope would people know this story and get the Cole Porter reference in a science thread.

Second, a "Type II" Dyson sphere (which is not Freeman Dyson's original concept of a vast number of habitats orbiting a central star in an enclosing orbit, but a single static spherical shell with the star at the center), which I believe is what you are referring to, is dynamically unstable.

The Ringworld is unstable, but a complete symmetric sphere is merely of neutral stability, like a ball bearing sitting on a flat surface. That is to say, if something starts it moving, it'll keep on moving, but it won't accelerate. So you'd still need to do some dynamical corrections, but you could take your time about them.

But why do we insist that the system of shrouds be 1 meter thick? Why not submillimeter thick? You make the screens out of the ASB equivalent of superconducting mylar film. Then you get several layers of solar power satelites freely orbiting around the sun, no rings needed.

I'm not imagining "habitats", I'm imaging ultrawispy solar collectors. Or mirrors bouncing most of the photons back into the sun. Although they're gonna radiate back out again sometime. This is why I was imagining that the shell of solar collectors is going to look like a red giant...eventually those solar collecters are going to be glowing red hot.

Well, I was using conventional materials; assuming just grinding up asteroids and vacuum cementing them into a primative shield. However, you're going to have a problem with your "ultrawispy solar collectors" or lightweight mirrors in that light pressure will continue to push them outward, and as you note, you'll still end up radiating at some point. Perhaps you could absorb solar energy and reradiate it as a laser in some some direction, but doing so would still produce waste heat that would have to be radiated away. Thermodynamics is such a bitch.

Quote:

Originally Posted by Chronos

The Ringworld is unstable, but a complete symmetric sphere is merely of neutral stability, like a ball bearing sitting on a flat surface. That is to say, if something starts it moving, it'll keep on moving, but it won't accelerate. So you'd still need to do some dynamical corrections, but you could take your time about them.

I was assuming that you'd spin the sphere for centrifugal force along some equator. Otherwise, you'll have to use some kind of gravity generators, or fill the entire volume with air at 1 atm, both of which pose major technical/logistical problems. Anyway, I'm pretty confident that nobody is really building Type II Dyson spheres, and find it pretty unlikely anybody is concealing stars (at least, via a material barrier) regardless of how advanced they are.

Now, a giant spherical graviational field which created an artificial event horizon (except for a small exit portal, of course)...that would be a terrific way to conceal a star. Of course, it would also have to be of extraordinary size and energy. It's probably easier just to paint it pink and erect a Somebody Else's Problem field around it.